Prostate cancer is the most common solid malignancy in men and the second most common cause of male cancer-specific mortality. Over the past fifteen years, the implementation of testing for prostate specific antigen (PSA) has revolutionized the diagnosis and treatment of this important disease. Moreover, emerging epidemiologic evidence suggests that the prostate cancer mortality rate is decreasing directly due to PSA screening. Current PSA testing methods remain both inconvenient and costly when applied to screening. Conservative estimates place the projected cost of PSA testing for screening purposes alone at greater than three billion dollars a year in the United States. These characteristics impact particularly on the population of low-income patients at high risk for prostate cancer who may be uninsured or live in underserved areas. We have designed a prototype biosensor chip for quantitating blood PSA levels. This chip is an amperometric immunosensor, which would form the core of an inexpensive handheld device for measuring PSA at the bedside or in the physician's office. A critical goal of this project will be to produce a fusion molecule that shares PSA immunoreactivity and glucose oxidase enzymatic activity. This conjugate molecule will compete with PSA at the chip surface and thereby couple immune recognition to an easily detectable electrical signal. A device of this type should significantly impact the diagnosis and treatment of prostate cancer by lowering the cost and broadening the availability of PSA testing for all patients at risk. This is of particular concern given the striking racial differences in prostate cancer mortality, which may be attributable to inadequate access to PSA screening in medically underserved populations.